For many purposes in agriculture and related endeavors it is desired to treat plants with exogenous chemical substances of various kinds. An exogenous chemical substance as defined herein is a chemical substance, whether naturally or synthetically obtained, which is applied to a plant to result in expressing a desired biological activity. By "biological activity" is meant the elicitation of a stimulatory, inhibitory, regulatory, therapeutic, toxic or lethal response in the plant or in a pathogen, parasite or feeding organism present in or on the plant. Examples of exogenous chemical substances include, but are not limited to, chemical pesticides (such as herbicides, fungicides, bactericides, viricides, insecticides, miticides, nematicides and molluscicides), plant growth regulators, fertilizers and nutrients, gametocides, defoliants, desiccants, mixtures thereof and the like.
Plants treatable by the process herein described are those classified as tracheophytes or vascular plants, i.e. those having a differentiated vascular or conducting system comprising phloem and xylem tissues. Vascular plants include pteridophtyes, gymnosperms and angiosperms. The process and compositions provided herein are particularly adapted for treatment of terrestrial plants, though aquatic plants that are semi-submerged or have leaves or fronds above water level can also be treated by such process and compositions.
Many exogenous chemical substances are applied to foliage (i.e. leaves and other non-woody above-ground parts) of a plant, and have a site of action in the plant either close to or remote from the locus of application. Such substances are referred to herein as foliar-applied exogenous chemical substances. Typically, by plant treatment processes known in the art, only a small portion of the amount of an exogenous chemical substance applied to foliage reaches sites of action in the plant where the biological effect of the exogenous chemical substance can be usefully expressed. It is therefore a major desideratum in agriculture and related endeavors to enhance the efficiency of delivery of foliar-applied exogenous chemical substances to their sites of action in plants, and thereby to enhance the biological effectiveness of the exogenous chemical substance for the purpose for which it is used.
Application to foliage of an exogenous chemical substance by processes known in the art does not universally result in inefficient delivery to sites of action. In some situations such processes provide excellent biological effectiveness, even at a low use rate of the exogenous chemical substance. In other situations the same processes, using the same rate of the exogenous chemical substance, provide inadequate biological effectiveness. Thus, these processes are inconsistent in the result they provide, or they cannot be relied upon to provide the desired result. The problem is that it is seldom possible to identify in advance those situations where good biological effectiveness will be obtained, partly because so many factors influence delivery efficiency. These factors include weather (temperature, relative humidity, daylength, cloudiness, precipitation, wind, etc.) preceding, during and following application, soil conditions (fertility, aeration, etc.), plant growth stage, health and physiological status, equipment-related inaccuracies in application, and other factors. Therefore, to help ensure reliable or consistent biological effectiveness of a foliar-applied exogenous chemical substance, the user typically applies the substance at a higher rate than truly necessary in the majority of situations.
Benefits of a process providing greater reliability of biological effectiveness include an ability to reduce rates of application of exogenous chemical substances without sacrificing consistency of biological effectiveness. Pressures felt by the agricultural industry to reduce pesticide, particularly herbicide, usage are well evidenced by symposia on the subject, such as that held in 1993 by the Weed Science Society of America and documented in Weed Technology 8, 331-386 (1994). Reduced use rates bring rewards not only environmentally but also economically, as the cost per unit area treated decreases.
A widely practiced method of enhancing reliability of biological effectiveness of a foliar-applied composition of an exogenous chemical substances, particularly a herbicide, is to add an enhancing agent comprising an ammonium salt, most commonly ammonium sulfate, to the composition being applied. It is well known to those practising this method that enhanced biological effectiveness is not assured with every use; however the low cost of the method means that even if biological effectiveness is enhanced in only a small proportion, for example 1 in 5, of times the method is used, it is still worthwhile.
There are limitations to the usefulness of ammonium salts as enhancing agents resulting from the relatively high rates that have to be used. Ammonium sulfate, for example, is typically used at concentrations in an aqueous application solution of 1-5% weight/volume, for example around 2% weight/volume. Common spraying equipment used in agriculture applies a spray volume of 50-1000 liters per hectare (l/ha) of solution;
at a typical spray volume of 200 l/ha containing 2% ammonium sulfate, the use rate of ammonium sulfate is 4 kg/ha. Such a high use rate leads to inconvenience for the user and difficulties for the formulator desiring to provide a product combining both an exogenous chemical substance and an enhancing agent based on ammonium sulfate.
Most exogenous chemical substances are designed to be used at much lower rates than those shown above for ammonium sulfate, for example 1-1000 grams of active ingredient per hectare (g a.i./ha). Thus, in an application process using ammonium sulfate, the amount of ammonium sulfate used is typically much greater than the amount of the exogenous chemical substance. It is consequently uneconomic in most situations for the manufacturer of the exogenous chemical substance to supply a useful amount of ammonium sulfate preformulated with the exogenous chemical substance. Economics in the agricultural pesticide business, for example, mandate that the pesticide be formulated at as high a concentration or loading as possible to minimize packaging, shipping and storage costs. The requirement to coformulate a large amount of ammonium sulfate with the pesticide active ingredient is inconsistent with achieving a high loading of active ingredient.
It is therefore an objective of the present invention to provide an agent that lo enhances the reliability of effectiveness of foliar applied exogenous chemical substances but that achieves this at much lower use rates than is the case with ammonium sulfate.
Many studies have been conducted in pursuit of this elusive goal. As biological effectiveness of an exogenous chemical substance depends upon delivery of the substance into living cells or tissues of the plant, some investigators have focused the search for a low-rate enhancing agent on classes of compounds which, at low rates, can be expected to stimulate various biological processes in plants. U.S. Pat. No. 4,436,547 to Sampson discloses that additives to improve the action of agricultural chemicals can include a carbohydrate source or organic acid to supply metabolizable energy or as precursors of amino acids and nucleotides, a vitamin or coenzyme to stimulate metabolic processes, a nucleic acid precursor to stimulate nucleic acid synthesis, a fatty acid (or fat or oil that can be degraded thereto) as precursor of molecules required in growth processes, an amino acid as structural unit for protein synthesis, and a naturally occurring plant growth regulator to affect metabolism in such a way as to render an applied pesticide more effective. In the case of herbicides, it is postulated in the above cited patent that "by stimulating growth and uptake of applied chemicals it is possible to enhance the activity of a number of herbicides, especially against older more established weeds."
The present invention provides a process for enhancing reliability of biological effectiveness of a foliar-applied exogenous chemical substance involving an enhancing agent not contemplated by Sampson, namely a phenyl-substituted olefin compound as herein defined.